Air bag system for automotive passenger seat

ABSTRACT

An air bag system for protecting a passenger seated on the front passenger seat of a vehicle. In an initial stage, the air bag is inflated mildly. In the subsequent stage, the bag is inflated also mildly. The directivity of produced gas can be reduced. The air bag can be inflated mildly while maintaining a large area. The air bag system comprises an air bag case having an opening on its top side, an inflator disposed inside the air bag case, the aforementioned air bag folded in the air bag case, and a diffuser mounted between the inflator and the opening in the case. The air bag is placed in a side-by-side relation to the inflator and located behind the inflator inside the case. The diffuser is provided with numerous holes for supplying the gas. The diffuser acts to regulate flow of the gas from the inflator. At least when the gas is produced from the inflator, a space is created between the outer surface of the inflator and the diffuser.

BACKGROUND OF THE INVENTION

The present invention relates to an air bag system for an automotivefront passenger seat and, more particularly, to an air bag system whichdetects a certain level of impact on collision of the automobile andcauses a gas to be produced from an inflator that is a gas generator soas to inflate an air bag, thus constraining a passenger seated on thefront passenger seat.

One kind of an air bag system for an automotive front passenger seat isa vertical type air bag system comprising an air bag case, an inflatormounted under the bag case, and an air bag mounted above it. In alateral type air bag system, an inflator is located on one side in anair bag case. An air bag and the inflator are arranged side by side in adirection parallel to the plane of the opening in the air bag case.Various lateral type air bag systems including this kind have beenproposed. These proposed systems are discussed in detail below.

One kind of lateral type air bag system has been devised by the presentapplicant and is described in Japanese Patent Laid-Open No. 191362/1994.This system has an air bag case which opens to a substantiallyhorizontal surface of an automotive instrument panel. An inflator and azigzag folded air bag are mounted inside the air bag case such that theinflator is positioned ahead of the bag, i.e., the inflator is locatedcloser to the front of the vehicle. An unfolded flat bag portion extendsover the inflator. The inflator is provided with gas support ports whichare located at a front upper position and a rear lower position,respectively, in a horizontal cross section of the inflator.

In the operation of this air bag system, when a gas is produced from theinflator, the unfolded flat bag portion which is located immediatelyabove the inflator begins to inflate. Therefore, the upper portion ofthe bag expands upward first and swells into the space defined by thewindshield extending obliquely and also by the instrument panel. As aresult, the upper portion of the air bag assumes a given shape.Subsequently, the lower portion of the air bag expands. Consequently,the whole bag expands into a desired three-dimensional shape.

An example of a method for folding an air bag is seen in an air bagsystem described in Japanese Patent Laid-Open No. 227353/1994, alsoinvented by the present applicant. An embodiment of this airbag systemis similar in structure to the air bag system described in theabove-cited Japanese Patent Laid-Open No. 191362/1994 except that an airbag disposed in a side-by-side relation to an inflator inside an air bagcase has an upper, zigzag folded portion adjacent to the inflator and alower portion which is adjacent to the upper portion and wound into aroll. When the gas is produced from the inflator, the zigzag foldedportion loosens more easily than the lower wound portion. By making useof this fact, the upper portion of the air bag expands first when thegas is produced from the inflator. Subsequently, the lower portionexpands. As a result, the whole structure swells into a desiredthree-dimensional shape.

These well-known techniques control the behavior of expansion of an airbag, by taking notice of the structure of a module.

In U.S. Pat. No. 5,405,164 (Japanese Utility Model No. 3014497), adiffuser is located over an inflator with a space between them. Thisinflator is shaped like a bottle. A gas is ejected from around a portformed at one side of the inflator. This is a so-called hybrid inflator.Since the gas injection portion is distributed unevenly in this way, thediffuser is mounted to regulate the flow of the gas from the port.Specifically, the diffuser is provided with minute holes in positionscorresponding to the opening in the inflator. The diameter of the holesincreases away from the opening.

Japanese Patent Publication No. 78052/1994 (U.S. Pat. No. 4,998,751)discloses a technique for causing an inflator to exhibit an S-shapedoutput characteristic curve. In particular, this publication says, “Itis an object of the present invention to provide an improved two-chamberexpansion system for imparting an S-shaped pressure-time performancecurve to an air bag which protects an automotive passenger. In thisexpansion system, charges of a gas-generating agent in the chambers aresimultaneously ignited by a single blasting device. It is a morespecific object of the present invention to provide a two-chamberexpansion system which delays ignition of the gas-generating agent inthe second chamber after the gas-generating agent in the first chamberis ignited, the expansion system being further characterized in that theduration of the delay is achieved by the structure and shape of theblasting device.” (column 7, lines 9-17). This system is capable ofexpanding the air bag slowly at first to mildly push the passenger if heor she is a child assuming an inappropriate posture. Then, a controlled,released gas is supplied into the air bag so as to expand the bagquickly to protect the seated passenger, irrespective of his or herbuild (column 17, lines 34-38). The output characteristic curve isshaped into an S-shaped form by adopting this inflator. That is, theoutput of the inflator can be made low at first. However, the effect ofthe S-shaped characteristic curve may be lessened, depending on thestructure of the module located downstream of the inflator as viewedfrom the injected gas stream. Furthermore, the bag is not expandedmildly throughout the process of expansion.

These air bag systems control the behavior of expansion of air bags, bytaking notice of only the inflator output and the regulation provided bythe diffuser.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide an air bagsystem which inflates an air bag mildly during its initial phase ofexpansion by finding a correlation between the inflator outputcharacteristic and a modular structure. It is a second object of theinvention to permit the air bag to be inflated mildly during all phasesof the inflation of the air bag.

The present invention is intended to achieve these objects. An air bagsystem is provided that includes an air bag case having an opening on atop side, an inflator disposed inside the air bag case, a folded air bagjuxtaposed to the inflator and disposed behind the inflator inside theair bag case (i.e., the air bag is located closer to the rear of thevehicle than the inflator), and a diffuser for regulating a stream of agas from the inflator. The diffuser is located between the inflator andthe opening in the air bag case, and is provided with a plurality of gassupply nozzles or holes. A space is created between the outer surface ofthe inflator and the diffuser at least when the gas is produced from theinflator.

The diffuser may be made of a metal or other rigid substance.Furthermore, the diffuser may be made of cloth or other soft material.In the latter case, when the air bag has been folded, the diffuser is inintimate contact with the outer surface of the inflator. However, whenthe gas is being produced from the inflator, the diffuser is alsoinflated, thus creating the space between the diffuser and the inflator.

Since this air bag system is equipped with the diffuser, the gas spoutedfrom the inflator is temporarily stored in the space between theinflator and the diffuser. The stored gas is mildly supplied as aregulated stream from openings in the diffuser into the air bag. Forthis purpose, the space between the inflator and the diffuser preferablyhas a volume adapted to temporarily store the gas produced from theinflator. Furthermore, it is desired to appropriately determine thenumber of the holes, or openings, in the diffuser, the total area of theholes, and their positional relationship. The amount of the gasexhausted is made uniform over the whole outer surface of the diffuser.

In another feature of this air bag system, the inflator and the air bagare arranged side by side. Consequently, the upper portion of the airbag is inflated first. Then, the lower portion is inflated. Hence, mildexpansion is accomplished.

The air bag disposed in the air bag system has a folded portion whichcan comprise an upper zigzag folded portion and a lower portion woundinto a roll. The upper portion is adjacent to the inflator. The lowerportion is adjacent to the upper portion. In this structure, when a gasis supplied into the air bag, the upper zigzag portion of the air baginflates first. Then, the lower coiled portion inflates. As aconsequence, milder expansion of the whole air bag is achieved.

This air bag system can be of a so-called top-mounted type. In thiscase, the opening in the air bag case lies in a substantially horizontalsurface of an instrument panel. Accordingly, the gas meets the surfaceof the flat portion located over the inflator, i.e., the unfoldedportion, and this portion first inflates. Then, this flat portion andthe following upper portion of the folded portion swell into a spacedefined by a windshield and the instrument panel. As a result, a desiredtwo-dimensional spread is obtained. Subsequently, the following lowerportion of the folded portion swells in such a way as to grow downwardsfrom the upper portion of the air bag inflated in two dimensions.Consequently, the air bag inflates into the desired three-dimensionalshape.

Let Q_(t) be the total amount of gas produced during a time intervalbetween 0 and t msec. Let A be the cross-sectional area of the openingin the air bag case. In this air bag system, the ratio Q_(t)/Apreferably varies in several stages as given below.0 msec Q ₀ /A=0 l/cm₂5 msec Q ₅ /A≦0.107 l/cm₂10 msec Q ₁₀ /A≦0.215 l/cm₂20 msec Q ₂₀ /A≦0.537 l/cm₂30 msec Q ₃₀ /A≦0.934 l/cm₂This makes it possible to inflate the whole air bag mildly. In the aboverelations, the total amount Q_(t) of the produced gas is an apparentvolume depending on the number of moles produced and amount of heat.

In this air bag system, the inflator may have two or more squibs(electric detonators). In this case, a delay time can be introduced inthe ignition time, and the output can be adjusted. More specifically,generation of the gas from the inflator is carried out in two stages. Asa consequence, the whole air bag is inflated more mildly. In addition,the inflator may also be a hybrid inflator having the two or more squibsas described above and two or more associated gas generators eachcontaining an explosive charge and a gas-generating agent. Thus, theinflator is charged with a compressed gas.

Generally, it is advantageous for this air bag system to use a so-calledhybrid inflator. Normally, heat is utilized to expand a gas. Inflatorsare broadly classified into two major categories: pyrotechnique inflatorand hybrid inflator. The former makes use of pyrotechnics, i.e.,explosive charges. Typical examples are described in the above-citedJapanese Patent Publication No. 78052/1994, in which an S-shaped curveis achieved with a pyrotechnique inflator. The latter consists of abottle-like container mainly charged with a pressurized gas and a gaspropellant, and is cited in the abovementioned U.S. Pat. No. 5,405,164.Specifically, a squib is mounted in the opening at one end of thebottle-like container. The squib is excited by an electrical signal.Then, a sagittal member disposed adjacent to the squib is moved axiallythrough the container. This breaks a pressure partition that isolatesthe pressurized gas from the outside atmosphere. Then, the pressurizedgas is produced through the opening and supplied into the air bag. Thesagittal member also acts on the explosive charge. The result is thatthe gas-generating agent placed around the explosive charge is reacted,thus giving heat to the pressurized gas. The expansion of the gas ispromoted further. In this way, the hybrid inflator is little assisted byheat during an initial phase of generation of the gas. This initialphase corresponds to the initial phase of the expansion of the airbag.Therefore, the output characteristic of the hybrid inflator producedduring this time interval is more easily adjusted mechanically anddimensionally than the pyrotechnique inflator which depends chiefly on achemical reaction.

On the other hand, where the diffuser is adjusted to adjust the gasfinally entering the air bag, it is necessary to adjust the volume ofthe space between the inflator and the diffuser. However, this approachhas limitations, since a space accommodating the bag must be secured.Furthermore, the total area of the nozzles or holes, their arrangement,and other factors must be adjusted. In this way, various limitationsexist. Accordingly, it is desired to adopt a hybrid inflator whoseoutput is easily matched to these limitations.

Other objects and features of the invention will appear in the course ofthe description thereof, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an air bag system according to thepresent invention in an assembled state taken along line I-I of FIG. 2;

FIG. 2 is an exploded perspective view of the air bag system shown inFIG. 1;

FIG. 3 is a cross-sectional view taken on line III-III of FIG. 2 of theair bag system in an assembled state;

FIG. 4 is a view similar to FIG. 1, but showing another embodiment ofthe air bag system according to the invention;

FIG. 5 is a view similar to FIG. 1, but showing a further embodiment ofthe air bag system according to the invention;

FIG. 6 is a view similar to FIG. 1, but showing a still other embodimentof the air bag system according to the invention;

FIG. 7 is a view similar to FIG. 1, but showing a yet other embodimentof the air bag system according to the invention; and

FIG. 8 shows a schematic of an inflator.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-3, there is shown an air bag system according tothe present invention. The air bag system is used for a passenger seatedon a front passenger seat of a vehicle. The system is located under theinstrument panel (not shown) which is substantially horizontal. Thesystem has an opening located immediately under the instrument panel.Indicated by W is the windshield, or front window, of the vehicle.

This system comprises a hybrid inflator 1, an air bag 2 inflated by agas from the inflator 1, and an air bag case 3 accommodating bothinflator 1 and air bag 2. The inflator 1 consists of a bottle havingholes 1 a in its neck. The case 3 is open at its top side. Inparticular, inside the air bag case 3, the inflator 1 is located on aside F of the front of the vehicle. The folded air bag 2 is located on aside R of the rear of the vehicle. That is, the bag 2 is positionedbehind the inflator 1. A diffuser 4 is mounted between the inflator 1and an interior of the air bag 2 to regulate flow of the gas from theinflator 1.

Since a position at which a top side of fringes 2 b of an opening in theair bag is ahead of the inflator 1, cloth on a top portion of the airbag 2 bridges across the inflator 1. A folded portion of the air bag 2is located behind the air bag 2. Therefore, the top portion of the airbag 2 can be first unfolded during operation.

In the air bag system, the diffuser 4 and a wall portion 3 a of the airbag case 3 together form a space 5 around the inflator 1. Extensions areformed at ends of the diffuser 4 to form retainers 6 which squeeze thefringes 2 b of the opening in the air bag 2 against the air bag case 3.Since the retainers 6 and the diffuser 4 are formed integrally in thisway, the system is made up of a fewer number of components thanconventional. Also, the system can be manufactured with a fewer numberof steps. In addition, the air bag 2 is quite easy to mount.

A bolt 1 b is mounted to a foot of the inflator 1, extends through theair bag case 3, and is fixed with a nut 7. The inflator gas is ejectedfrom holes 1 a which are distributed unevenly. The ejected gas isregulated by holes 4 a in the diffuser 4, as shown in FIG. 3, and issupplied into the air bag 2. The diffuser 4 is a curved regulator plateand covers the outer surface of the inflator 1 mounted in the air bagcase 3 with the given space 5 left around the inflator 1. Depending onthe positional relation of the diffuser 4 to the inflator 1, thediffuser 4 may be flat. The holes 4 a formed in the surface of thediffuser 4 are distributed in a given manner to supply the gas streaminto the air bag 2 uniformly. The gas released from the inflator is oncestopped and stored in this space. Then, the regulated gas stream ismildly supplied from the surface of the diffuser 4 into the air bag 2.The flow rate of the gas supplied into the air bag 2 is varied inseveral stages, by adjusting the volume of the space 5, the number ofthe holes 1 a, and a total area of the holes 4 a while maintaining abalance with the output characteristic of the inflator. The air bag 2 ismildly inflated during its initial phase of expansion. The air bag 2 isinflated also mildly during the subsequent phase. Generally, withrespect to the holes 4 a in the diffuser 4, many smaller holes arepositioned close to the holes 1 a in the inflator 1 and comparativelylarge fewer holes are located remotely from the inflator holes 1 a. Thisstructure is desirable for regulation of the gas supplied into the airbag 2.

The inflator 1 is cylindrical in shape. In this inflator 1, thegas-generating agent is ignited. The resulting pressure and heat releasethe pressurized gas from the container. The inflator 1 is a so-calledhybrid inflator.

As described above, the air bag opening that is an inlet port forintroducing the gas into the air bag 2 may be fixed to the air bag caseopening. Instead, the opening may be wound around the inflator as shownin FIG. 5. The air bag 2 in FIG. 5 is otherwise folded in a manner asshown in FIG. 1. That is, each folded portion extends substantiallyhorizontally. Referring again to FIGS. 1-3, an upper portion of the airbag 2 is folded in a zigzag fashion. A following lower portion is woundinto a roll, a wound portion a, and is received on the bottom of the airbag case 3. The zigzag folded portion b is received near the opening inthe air bag case 3. The zigzag folded portion b terminates in a flat,unfolded portion c which is close to the opening in the air bag 2. Theportion c bridges over the inflator 1. The upper side of the fringe 2 bof the opening in the air bag 2 is held between the retainers 6 and 6′mounted to a front wall of the air bag case 2 and the inflator,respectively. Since the air bag 2 is folded and wound in this way, theflat portion c is first unfolded obliquely upwardly and rearwardly alongthe windshield W. These portions are unfolded in this order. Since theseportions are successively inflated in this manner, mild expansion isaccomplished throughout the whole inflation process.

With respect to the contour of the opening in the air bag case 3, thedimension taken longitudinally of the vehicle is preferably in excess of120 mm, and the dimension taken across the vehicle is preferably inexcess of 190 mm. In this case, the area A of the opening in the air bagcase 3 is greater than 228 cm². It is desired to set the depth of thecase, or dimension taken vertically of the vehicle, to about 100 mm,taking account of the diameter of the inflator, the space accommodatingthe air bag 2, and the volume of the folded air bag 2.

In this system, the generated gas which is supplied from the opening inthe air bag case 3 into the air bag 2 through the diffuser 4 expandsaccording to the number of moles and amount of heat. The amount of gaspassing through the opening in the air bag case 3 divided by thecross-sectional area of the air bag case 3, i.e., Q_(t)/A where Q_(t) isthe total amount of gas produced during a time interval from 0 to tmsec, and A (A≧228 cm²) is the area of the opening in the air bag case3, varies with time in several stages as follows:0 msec Q0/A=0 l/cm²5 msec Q5/A≦0.107 l/cm²10 msec Q10/A≦0.215 l/cm²20 msec Q20/A≦0.537 l/cm²30 msec Q30/A≦0.934 l/cm²

In this way, in the above-described embodiment, the gas is suppliedmildly. The gas is supplied into the upper portion of the air bag 2 toinflate the upper portion first. Then, the lower portion is expanded.Therefore, during its initial phase of the expansion, the air bag 2 isinflated in several phases over the instrument panel while maintainingthe wide area of the inflated air bag efficiently. The air bag 2inflates so as to surround the instrument panel. The extent of expansionis made large efficiently. The whole air bag 2 can be inflated graduallywith a large area. Therefore, the directivity of the expansion of theair bag 2 is reduced. This permits the air bag 2 to inflate mildly.

The system may also incorporate a module using an inflator 1 having twosquibs 60 as shown in FIG. 8. A delay time is introduced in the ignitiontime to adjust the output.

Referring next to FIG. 4, there is shown another embodiment of theinvention. Like parts are indicated by like reference numerals in theembodiment of FIGS. 1-3 and also in the embodiment of FIG. 4, butnumeral 10 is added to the numerals used in FIG. 4.

In this embodiment, an air bag case 13 assumes a boxlike shape. Adiffuser 14 of a cross section consisting of about three quarters of acircle is mounted around an inflator 11 with a space 15 between them. Anair bag 2 is composed of an upper portion b and a lower portion a. Whenthe air bag 2 is folded, the upper portion b is folded in a zigzagfashion and the lower portion a is wound into a roll, in the same way asin the case of FIG. 1. A flat, unfolded portion c exists near theopening in the case 13. At one end of the flat portion c, i.e., theupper side of the fringe 2 b of the opening in the air bag 2, is securedwith a bolt and a nut to an upper end of a left side wall of the case 13as viewed in the figure. The lower side of the fringe 2 b of the openingin the air bag 2 is similarly anchored to an upper side of a right sidewall of the case 13.

An embodiment shown in FIG. 5 is similar to the embodiment of FIG. 4. InFIG. 5, the like reference numerals to which 10 is added are replaced bythe like reference numerals to which 20 is added. This embodiment ischaracterized in that an air bag 22 is provided with no opening. Aninflator 21 and a surrounding diffuser 24 are disposed inside the airbag 22. The inflator 21 and the diffuser 24 are fastened to the air bagcase 23 by means (not shown).

Referring to FIG. 6, there is shown a still other embodiment of theinvention. In FIG. 6, those parts which correspond to like parts of theembodiment of FIG. 1 are indicated by like reference numerals to which30 is added. This embodiment is characterized in that an air bag 32 isfolded not horizontally but vertically, unlike the above embodiments. Anair bag portion b′ adjacent to an inflator 33 is folded in a zigzagmanner, and an adjacent portion a is wound into a roll. An air bagportion c extending from the portion of the folded portion b′ closest tothe inflator 33 to the upper side of the fringe in the opening in theair bag is not folded but kept flat.

The air bag 32 is disposed in a side-by-side relation to the inflatorinside the air bag case. The manner in which the air bag 32 is foldedand wound is not limited to the foregoing method. As shown in FIG. 7,the whole air bag 42 can be folded in a zigzag manner as indicated by b.Furthermore, the whole air bag 42 may be wound into a roll (not shown).The air bag case has a door D.

In the present invention, an air bag is inflated mildly in an initialstage. This makes the subsequent expansion milder. Furthermore, thedirectivity of the gas can be diminished. Therefore, the air bag can beexpanded into a desired shape mildly while maintaining a large area.

1. An air bag system for use in a vehicle, comprising: an air bag case having an opening on its top side; an inflator disposed inside said air bag case and having an outer surface; a folded air bag arranged in a side-by-side relation to said inflator and located behind said inflator inside said air bag case; a diffuser mounted between said inflator and said opening in said air bag case and provided with a plurality of gas supply holes, said diffuser acting to regulate flow of a gas from said inflator; and a space created between the outer surface of said inflator and said diffuser at least when the gas is produced from said inflator. 